Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Much below critical temperature

At critical Temperature

Above critical temperature

3. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Carbon dioxide

Ammonia

Freon

4. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

5. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Wet vapour

Saturated liquid

Dry saturated vapour

6. The vapour compression refrigerator employs the following cycle

Rankine

Carnot

Reversed Carnot

Reversed Rankine

7. A bootstrap air cooling system has

One heat exchanger

Two heat exchangers

Four heat exchangers

Three heat exchangers

8. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

Super-cooling

None of these

Normal cooling

9. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

10. Most thermostatic expansion valves are set for a superheat of

15°C

10°C

20°C

5°C

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11. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

15 bar

2 bar

30 bar

12. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.376

0.67

0.4

13. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

14. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Condenser tubes

Refrigerant cooling tubes

Evaporator tubes

15. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Any one of the above

Always more than unity

Always less than unity

16. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

17. In a refrigeration system, the expansion device is connected between the

Evaporator and compressor

Condenser and receiver

Compressor and condenser

Receiver and evaporator

18. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant pressure

Takes place at constant temperature

Takes place at constant entropy

19. In a lithium bromide absorption refrigeration system

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

Water is used as a refrigerant and lithium bromide as an absorbent

20. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

1.33

4.33

3.33

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21. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Less

Same

22. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

23. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

None of the above

24. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

5.12

2.15

25. Which of the following is not a desirable property of a refrigerant?

Low boiling point

Large latent heat

Good electrical conductor

High risibility with oil

26. The boiling point of ammonia is

-10.5°C

-30°C

-33.3°C

-77.7°C

27. The domestic refrigerator uses following type of compressor

Axial

Miniature sealed unit

Centrifugal

Piston type reciprocating

28. The freezing point of sulphur dioxide is

-77.7°C

-135.8°C

-56.6°C

-75.2°C

29. For obtaining high COP, the pressure range of compressor should be

Any value

High

Optimum

Low

30. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Dry bulb temperature of air

Dew point temperature of air

Wet bulb temperature of air

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31. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

32. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

1: 9

1: 3

9: 1

33. The curved lines on a psychrometric chart indicates

Relative humidity

Dry bulb temperature

Wet bulb temperature

Dew point temperature

34. Critical temperature is the temperature above which

Water will never evaporate

Water will evaporate

A gas will immediately liquefy

A gas will never liquefy

35. Rating of a domestic refrigerator is of the order of

40 tons

10 tons

5 tons

0.1 ton

36. Cooling water is required for following equipment in ammonia absorption plant

Evaporator

Condenser, absorber and separator (rectifier)

Condenser

Absorber

37. The capillary tube, as an expansion device, is used in

Domestic refrigerators

Water coolers

Room air conditioners

All of these

38. Which of the following cycles uses air as the refrigerant?

Carnot

Stirling

Ericson

Bell Coleman

39. Freon group of refrigerants are

Toxic

Inflammable

Non-inflammable and toxic

Nontoxic and non-inflammable

40. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

None of these

Zero

Positive

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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